1. Field of the Invention
The present invention relates to a method and apparatus for connecting an integrated circuit to an external system, such as a test and burn-in system. More particularly, the present invention relates to the use of flexible conductive structures for performing test and burn-in of integrated circuit packages with ball grid arrays.
2. Description of the Related Art
Integrated circuit packages generally include internal and external structures utilized to electrically connect integrated circuits to external circuitry. One known type of integrated circuit package is a ball grid array ("BGA") package. BGA packages include an array of solder balls in a selected pattern on an external portion of the package. The solder balls are placed on metallic portions of external circuitry, such as a circuit board, and heated. Upon solidifying, the solder balls form conductive metal-to-metal bonds with the circuitry.
BGA packages are referred to in U.S. Pat. No. 5,796,163 (Glenn et al.), U.S. Pat. No. 5,716,222 (Murphy), and U.S. Pat. No. 5,831,832 (Gillette et al.). In Murphy and Gillette et al., the solder balls have rigid, solderable coverings. A potential problem with such a design is the creation of defects caused by fitting the coverings over the solder balls. Another potential problem is a loosening of the fit of the coverings over the solder balls, thus diminishing the electrical connections therebetween.
Prior to releasing an integrated circuit package for public use, it may be necessary to test and/or "burn-in" the integrated circuit. The procedure may be used to stabilize the characteristics of the integrated circuit die and reveal any defects therein.
One method for testing an integrated circuit package having a ball grid array is through the use of a plurality of silicon pillars on a test apparatus. The silicon pillars, which are electrically conductive, are placed in contact with the solder balls of the integrated circuit package to test or burn-in the package. The pillars provide electrical connections between the test apparatus and the individual elements of the ball grid array. A problem with utilizing silicon pillars, however, is their lack of flexibility. Due to their lack of flexibility, the silicon pillars may damage the solder balls on contact, thereby creating defects in the integrated circuit package. Damage sustained by the solder balls is due to excessive deformation, which results in decreased ability to solder.
U.S. Pat. No. 5,475,317 (Smith) refers to a conductive elastomeric probe which is screened onto bond pads used to test a singulated bare die. The elastomeric probes are used to ensure electrical connectivity. The invention described in Smith is directed to the testing of dies earlier on in the processing of the dies. The Smith patent does not suggest testing of dies which are further along the processing line, and it does not discuss the testing of dies which utilize solder balls.